This invention relates to a low-pressure discharge lamp comprising a discharge tube and a base providing for the electrical and mechanical connection of the lamp. It also relates to a lampholder of the low-pressure discharge lamp.
Low-pressure discharge lamps are known which comprise a discharge tube provided with a gas-tight seal at its ends and defining a discharge space, and a housing comprising a cap fixing the ends of the discharge tube and a base part. The best known form of the so-called compact fluorescent lamps of this type is in which the discharge tube is U-shaped. Low-pressure discharge lamps using this form of the discharge tube can be known, e.g. from U.S. Pat. No. 5,446,340. The characteristic feature of this discharge lamp is that the discharge tube consists of straight portions, arc-shaped portions connecting the straight portions and bridges. The straight portions are parallel both to each other and to the longitudinal axis of the lamp. Since the discharge tubes are arranged in space in these solutions in order that they can be connected, the disadvantage of this tube construction is that the lamps are xe2x80x9chighxe2x80x9d (long) and broad at the same time which is unfavorable in some fields of application.
Solutions, in which the discharge tube is bent to have a bi-directional spiral, i.e. a so-called helical form, are aimed at decreasing the height size of the lamp with the consequence that the height of the discharge tube and, together with this, that of the discharge lamp is also decreased. Such a solution can be known, e.g. from U.S. Pat. No. 5,675,215 where the height of the lamp is smaller than that of the U-shaped tubes but still exceeds its width.
In some fields of application, a demand for low-pressure discharge lamps with a very small height appeared wherein the lamp extends substantially only in two dimensions rather than three. In order to meet this requirement, ring-shaped discharge lamps were developed and among these, the lamps having so-called 2D-shaped discharge tubes have proven to be the most advantageous. A discharge lamp of this type is disclosed in patent specification No. EP 0 0057 974. In this, the known discharge tube also comprises straight and arc-shaped portions but these are formed substantially in the plane perpendicular to the height of the lamp, while the base is constructed in the direction of the height of the lamp and can be inserted in a lampholder being outside the plane of the discharge tube. The disadvantage of this solution is that the base and the lampholder protruding from the plane of the bent tube still require a substantial amount of space which restricts its field of application.
Thus there is a particular need for further decreasing the height of the discharge lamp having a discharge tube of 2D or similar shape and extending in a plane perpendicular to the height of the lamp, which lamp requires even less space than the prior art lamps.
According to a first aspect of the invention, a discharge lamp including a discharge tube and a base ensuring mechanical and electrical connection of the lamp and connected to the discharge tube is provided. The discharge tube sealed in a gas-tight manner at its both ends is bent in substantially one plane so that the discharge tube has straight and arc-shaped portions, and the base connected to the ends of the discharge tube includes at least cathode leads of the discharge tube and electrical connectors connected to said leads. At least one component providing for mechanical connection to a lampholder is formed on the base. Each component of the discharge lamp ensuring mechanical connection to the lampholder is placed in a space bordered by the discharge tube.
In accordance with another aspect of the present invention, a lampholder of a low-pressure discharge lamp is provided, and the lampholder has components ensuring electrical and mechanical connection to the discharge lamp having a discharge tube and a base. In a position in which the lampholder is connected to the discharge lamp, the components of the lampholder providing for mechanical connection to the discharge lamp are placed in a space bordered by the discharge tube.
An advantage of the present invention is that the height of the lamp having a discharge tube extending substantially one plane can be significantly decreased while preserving the necessary functions of the lamp. It is a further advantage that the base is made of a minimum amount of material and comprises only the inevitable components.